Coating compositions



Feb 7, l967 KEISUKE HxRosE ETAL 3,303,154

COATING COMPOS ITIONS Filed 0G13. 14, 1963 TETRAFLUOROETHYLENE MOL O/O INVENTORS KEISUKE HIROSE MASA() HASEGWA SHINICHI FUJIMAKI BY Mw, Ml l ATTORNEYS United States Patent O 3,303,154 COATING COMPOSITIONS Keisuke Hit-ose and Masao Hasegawa, Yokohama, and Shinichi Fujimaki, Ashiya-shi, Japan, assignors to Nitto Chemical Industry Co., Ltd., Tokyo, Japan Filed Oct. 14, 1963, Ser. No. 315,898 Claims priority, application Japan, Oct. 18, 1962, 37/45,179 7 Claims. (Cl. 26o-29.6)

The present invention relates to an improved coating composition of a fiuorine containing resin.

Hitherto, as one of surface treatments for metals and the like, coating by various resins has been utilized. In these coating materials, so-called uorine containing resins, such as, polytetrafluoroethylene resin,rpolytriuorochloro ethylene resin and the fluorine containing copolymer resins thereof show excellent properties in chemical resist'- ance and heat resistance, however since the uorine containing resins have no general solvents that can be used at room temperature for coating the resins, the resins cannot be used for surface coating as coating materials in a solution state. In general, a process has been carried out wherein the finely granulated resin is dispersed in water or organic solvents, it is coated on the surface of a body, the body is heated to evaporate ofrr the dispersing medium and the body is sintered in a furnace at above the melting point to weld lthe resin.

. However, as these uorine containing resins have a high viscosity at the melting p-oint and the adhesion of the resins tothe surface of metals and the like to be treated is poor, the coating operation is difficult. Since, in the polytetraluoroethylene resin, it is necessary in general to use a harmful primer and the thickness of coated lm in one operation is at most Q01-0.02 mm. even if the primer is used, it is difcult to form coated film without pinholes. Moreover the adhesive power of the coated film on a surface is not too strong but also the lm is peeled easily. While in the case of a copolymer resin of tetrafluoroethylene and vhexauoropropylene the adhesive property can be improved by using a primer, in order to obtain coated lm of a useful thickness the coating process must be repeated several' times, because the thickness of its coated film by one coating operation is thin. Also, since foams are liable to form locally in the case of spray coating, it requires great skill in operation. In the case of using a trifluorochloroethylene resin also, the thickness of the film by one coatingoperation is at most 0.1 mm. yeven if a primer is used and therefore, in order to obtain a desired thickness of coating of 0.3-0.5 mm. in, e.g., co-rrosion resisting coating of a reaction vessel, coating must be repeated several times.

When tetraliuoroethylene-ethylene copolymers, which contain 30-70 mol percent of ethylene, obtained by an emulsion polymerization in an aqueous medium containing a small amount of alcohol is dispersed in a dispersion medium yand coating is carried out by using thus obtained dispersoid, a lm having 0.1-0.2 mm. in thickness is formed by one coating operation without using a primer. However, as the sintering temperature of the copolymer resin is 2SC-290 C., and coated articles must be heated in air for a considerable time when the sizes of the articles are large, the coated lm would be caused to discolor by oxidation of air.

' A general object of this invention is referred with methods to obtain the coated lm to metal substrate.

A further object of this invention is to obtain a coating dispersoid for forming coated film that can be used stably without trouble up to 150 C. and have suicient resistances to all inorganic acids and organic solvents.

-A still further object of this invention is to obtain a uorine containing resin dispersoid that can be sintered at to increase resistance only.

3,303,154 Patented Feb. 7, 1967 ICC a lower temperature to prevent the degradation by air, besides fulfilling the above object. That is, the object is to lower the molding temperature or sintering temperature without reducing the" heat resistance and chemical resistance.

The inventors have found that the above objects can be attained by using for coating a dispersoid prepared by dispersing in a known dispersing medium a three-component copolymer which is prepared by the emulsion polymerization of tetrafluoroethylene and ethylene with the addition of isobutylene. The amounts of tetratluoroethylene, ethylene and isobutylene in the copolymer may be changed in a broad range according to the uses but for the -objects of this invention, it is preferable to use the compositions in the domain shown by oblique lines in the attached drawing which shows a composition system of a three-component copolymer for coating. The compositions in the domain can be shown by the following expressions:

In the condition of a+b-l-c=100% a20% ac bl.0%, cl.0%

tetrailuoroethylene-hexafluoropropylene copolymer resin.v

That is, it has an excellent resistance to organic chemicals, the melt viscosity of the resin at sintering temperature is very low, a at film can be formed without pin holes from the resin even at sintering temperature of Z50-270 C., the adhesion to metals is strong and coated lm having the adequate thickness can be easily formed by one coating operation. As in the part B resin, which is a part containing a large amount of isobutylene and tetrafluoroethylene, the orientation of the main chain is disturbed by the influence of the methyl group in isobutylene, the secondorder transition point `of the resin obtained by the measurement of dynamic Visco-elasticity is SO- C. which shows that the resin is in appearance softer thanvthe resin in the A part. The resin in the Bidomain is superior to the resin in the A domain in resistivity to inorganic acids, and discoloration by fuming sulfuric acid Ais particularly low. Further, as the content of tetrafluoroethylene is high, the property not to stick on the surface of an Aarticle or non-tackiness is increased though adhesion is weakened r to some extent.

The C part is the critical domain showing high adhesion and thick-film forming ability which are the great features of this invention in the case of coating metal surfaces, etc., by these three-component copolymer. In other part except A, B, and C, the properties of the resins are almost similar to those of polyethylene, though the presence of tetrafluoroethylene as comonomer contributes It has not particular influences on the increase of adhesivity. Further, in this domain the resistance to organic solvents is reduced, for example, the resins in this domain are dissolved at a high temperature in a solvent for polyethylene, such as xylene, so they show no novel properties as coating composition for chemical resistances even though they are a little resistant to chemical and heat compared t0 polyethylene resins.

That is, in only the domain shown by the oblique lines in the drawing are obtained coating composition having improved thick-film forming ability, strong adhesion to metal surfaces, heat resistance and chemical resistance.

In order to obtain such coating resins having the abovementioned improved properties, it is necessary that the size of the resin particles is extremely small and the dispersoid of the resin is prepared easily, and for the purposes it is desirable to use a polymer prepared by an emulsion polymerization.

When the emulsion polymerization yis carried out in an aqueous medium containing a small amount of an alcohol, the rate of polymerization is high and a stable latex can be obtained. For example, the following materials are placed in a 300 ml reaction vessel of stainless steel.

v G. Water 150 Tertiary butanol 4.5 Sodium borate 0.15 Ammonium persulfate 0.15 Ammonium rsalt of perfluorooctanoic `0.5 Dodecyl-mercaptan 0.15

The vessel is closed and a gas mixture of tetrafluoroethylene and ethylene having a mol ratio of 50/ 50 added with 3 mol percent of isobutylene is introduced. The system begins to agitate at 75 C. and 68.5 atmosphere. The polymerization proceeds as well as the pressure is reduced. When the pressure of the system is reduced to 45 atmosphere, an additional gas mixture having the above composition is added into the system to increase the pressure to 68.5 atmosphere.

Such a process is repeated and after 50 minutes the agitation is stopped. Unreacted gases remaining in the polymerizing vessel are discharged, and the product is withdrawn. By the process, 218 g. of a milk-White stable latex containing 11.7 weight percent of a three-component copolymer is obtained. The composition of the obtained copolymer is determined by measuring the change of monomer compositions before and after the reaction by means of gas chromatography, elementary analysis and infrared ray absorption spectrum analysis of the copolymer. The latex particles were confirmed by an electron microscopic observation to be homogeneous spherical particles of 0.05-0.l5 ma in diameter.

By aggregation and drying in the subsequent treatments, the particles of 0.05-0.15 mp. in diameter in the dispersoid are aggregated into particles of 3 to 5 ma in diameter. Thus a particle size of the copolymer is not easily obtained without the use of the emulsion polymerization and by using the copolymer prepared by the emulsion polymerization, the stable dispersoid of the copolymer can be prepared easily.

The latex of the copolymer obtained by the abovementioned process may be mixed with emulsion stabilizing agents, concentrated and coated on the surface of an article by spraying or dipping as an aqueous dispersoid. But, it is preferable for surface coating to separate the copolymer by solidfying the latex, drying the separated copolymer and then dispersing the copolymer in a volatile organic solvent.

For example, the latex prepared by the above-mentioned polymerization method is solidified by a freezing process, washed with hot water and an alcohol, and dried in vacuo at 50 C. to afford 25 g. of the white powder of the three-component copolymer. The polymer powder is, in a concentration of l0 'to 50 Weight percent, added into an organic dispersing medium, such as, alcohols, e.g., methanol, ethanol, propanol, butanol and cyclohexanol; esters, e.g., ethyl acetate, butyl acetate and amyl acetate; ketones, e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; aromatic hydrocarbons, e.g., benzene, xylene and toluene; and halogenated hydrocarbons, e.g., carbon tetrachloride, trichloroethane, trichloroethylene and perchloroethylene.

The mixture is then agitated in an agitator capable of high-speed agitation to give a dispersoid suitable for coating. Further, if the volatile rate of the above-described organic medium is too high, the medium may be used as a two-component dispersing medium by the addition of 5 t-o 30- weight percent of a high boiling point material such as cyclohexanol. Also, in order to prevent the oxidation and discoloration of the polymer at the sintering temperature, stabilizers or antioxidants of 0.1

to 5.0l weight percent based on the polymer may be added. As various pigments, reinforcing agents and additives, carbon black, inorganic oxides or fine particles, etc., may be added. By the results of our experiments it has been found that a dispersoid of a mixture of a mixed solvent of 9 parts by weight of carbon tetrachloride and 1 part by weight of cyclohexanol, and 15 to 20% by weight of the three-component copolymer powder obtained by the above-mentioned method containing 1% by weight based on the resin of dicyclohexylamine is particularly suitable as a coating dispersoid by spraying and dipping.

The coated film obtained from thus prepared dispersoid show strong adhesion that has never been obtained by conventional polyethylene or polytetrafluoroethylene resins. In other words, the film coated by spraying on iron plates, aluminum plates or stainless steel plates adheres strongly to the surface of the metal without applying any surface treatment afterward and it is impossible to peel off by means of a knife or a blade the resin film from the contact surface. While the three-com ponent copolymer has a small dielectric'loss similar to that of a polyte'trafiuoroethylene resin in a broad frequenvcy range and the copolymer is considered to be a nonpolar polymer, it adheres strongly to metals.' It is not clear that the adhesive property of a resin film is influenced by only physical adhesion caused by the surface condition of a metal to be coated or by chemical bonding besides,'but polyethylene coated film can be peeled by means of knives, polytetrafiuoroethylene coating can be easily peeled off even by using a primer, and tetrafluoroethylene-hexauoropropylene copolymer coated film can be, even though it adheres comparatively strongly by using a primer, peeled from the contact surface by means of a knife or a blade. On the other hand, coating -by the three-component copolymer by this invention shows excel-lent adhesion, which is a lgreat feature of this invention. Further, other features of this invention is that since a dispersoid containing the material subjected to a specific treatment as sealer (primer) as in the case of other uorine containing resins is unnecessary in this invention, the 'resin'obtained by this invention is dispersed by using a low-price and general dispersing medium having almost no corrosive action and dangerous property without necessity of any treatment for increasing the adhesion of the resin dispersoid. Also, as shown in the later examples, such thickness of coated film formed -by one spraying or dipping step is one that has never been seen in coatings by conventional synthetic resins containing uorine. The usual thickness of coated film by one coating operation in this invention is '0.15 to 0.2 mm. and after the rst coat-ing operation, coated film of 0.2 to 0.3 min. can be formed by each additional coating operation. Therefore, a practical Icoated film thickness of 0.35 to 0.5 mm. can be obtained by only two coating operations. By reducing the number of the coating operations the operation time and consequently heating time are reduced, and then the deterioration of the resin, which is cause-d by degradation of polymer molecules at high temperature, can be prevented. Such a property is not seen in conventional fluorine containing resins, and it is also one of the features of this invention that such a uorine containing resin coated film having improved heat resistance and chemical resistance can Ibe formed easily and with a low cost.

In the three-component copolymervof this invention, the melting temperature can be reduced without changing substantially the thermal decomposition temperature of a two-component copolymer of tetralluoroethylene and 6 washed with warm water and warm alcohol 2 times each with stirring vand dried for one day at 120 C. to give 1,100 parts of the white timely-divided solid.

50 g. of thus obtained three-component copolymer ethylene. By the results of measuring the melting point 5 resin powder, 180 g. of car-bon tetrachloride, 20 g. of of the resins by a differential thermal analysis, the-"co cyclohexanol and 0.5 g. dicyclohexylamine were mixed bypolymer of this invention does not show a distinct melting means of a domestic mixer to lafford the coating dispoint as seen in high density polyethylene or polytetrapersoid. The dispersoid was spray-coated on the filed uoroethylene but the melting point of a two-component surface of an aluminum plate (50 x 100 X 3 mm?) by copolymer of tetrauoroethylene and ethylene in a 40/ 60 10 means of a spray gun of 0.7 mm. in an aperture by utilizmol ratio is from 240 to 250 C. and that of the threeing an air pressure of 25 kg./sg. cm. and `after evapocomponent copolymer added with 3 mol percent of isorating off the dispersion medium by maintaining the butylene is from 210-230o C. plate for 10 minutes at 150 C., the plate was placed for On the other hand, as the thermal decomposition temminutes at 260 C. in a sintering furnace to give a perature of both copolymers are about 290 C. and the 15 flat resin coated nlm of 0.15-0.20 in thickness of sintering temperature can be lowered in the case of the the t-hree-component copolymer on the surljace of the three-component copolymer, the heat deterioration can aluminum plate. IBy repeating the same process 2 times, be prevented. Further, as the copolymer can be sintered the resin film of 0.3-0.4 mm. in thickness having no pin at a comparatively low temperature, the antioxidation holes was obtained and by repeating 3 times the lm of effect by dicyclohexylamine, etc., can be increased more 0.5-0.6 mm. having no pin holes was obtained. The iilm remarkably. In addition, near the melting point the viscould not be peeled olf by means of a knife or a bliade. cosity of the three-component copolymer is reduced to Example 2 one severalty by the addition of isobutylene. Due to these 3 Y reasons, the three-component copolymer of this inven- .A sarid'bl'asteq 1m .Plate (.50 X .100 X 2 mm' was tion can easily afford a flat coated film having no pin dipped m the dlspersold Obtained m Example 1' Thf holes even by sintering almost without being affected by plate was, Wlthdrawn Slowly dried for 1,0 mmutes at 150 the thermal decomposition C. and smtered for 15 minutes lat 260 toafford flat The dispersoid by this invention is in particular useful coated mm of 01 mm' m thlckness 'having 'no Pmholes' forA surface coating of metals, such as, iron, aluminum, Example 3 I stainless steel and the like, but a lm of the copolymer Steel plates (50 X 1:00 mme) of 2 mm. in .thicknss` een b e Produced by eeatmg the copolymer en e'base bent into an L shape (the radius of curvature was about mateflal" Such es glass Plates and Peeling 'by a Sultable 1.5 mm.) were coated with the dispersoid obtained in method- Example 1 and, with la dispersoid of a copolymer of The examples ef thle mventlon are 3.5 fellows: tetrauoroethylene and bexauoropropylene. l At that, Example l the surfaces of the steel plates were cleaned with solvent but other surface treatment by, e.g., sand-blast or emery The following materials were placed in a horizontal cloths was not applied. agitation type polymerizing Vessel of 10 1. in inside vol- The coating conditions and the properties of the obume. tained resin coated nlm were as follows:

Dispersoid A B C Tetrafluoroethylene- Tetrafluoroethylene ethylene-isobutylene hexaliuoropropylene Same as (B) copolymer (same asin copolymer dispersoid Example 1) Primer Not used Used Not used. Spraying N o 4 time 4 times 4 times. num thickness 0.41%().45 mm 0.2e0-25 mm d20-0.25 mm. Appearance of the film No pinholes No pinholes. Locally some No pinholes.

foams at the bent part.

Parts The resin coated lm in the case C wherein no primer Water 6,300 was used began to peel 1 day Vafter sintering from the Tertiary butanol 190 metal ysurface at the bent part and the edges. It was Sodium borate 32.5 considered that the shrinking power of the resin by cool- Ammonium persulfate 6.5 6() ing was stronger than the adhesive power. The adhesion Potassium salt of pertluorooctanoic acid 13.0 to the metals of the coated lm in cases A and B was Dodecylmercaptan 6.5 very strong and ywhen a heat treatment of heating for After closing the vessel and completely purging air from 30 minutes at 150 C- and then quenching in Cold Water the vessel, a mixed gas of tetranuoroethylene and ethylwas repeated 10 times, n0 Changes were Observed. When ene in a mol ratio of 40:60 together Wit-h 3 mol percent 65 the coated film in case C was lined by ya blade, the lm of isobutylene was introduced into the vessel. When the was peeled easily as a band. In case B, the resin could system was agitated at C. and 30 atmosphere, the be peeled from the contact `surface even though it was Polymerization Pfoeeeded and the PfCSSnfe Was reducen not so easy as case C, while it was completely imp-os- Then an additive gas mixture having the above composlsible to peel the 51m in Case A. tion was added into the system to maintain the pressure 70 to 30 atmosphere at 70 C. After 2 hours, the agitation Example 4 was stopped, gases in the Vessel were removed and the product was withdrawn. A translucent, milk-white and Aluminum r0(15 0f 1045 X 50 'Inm- We'l'e Coated Wln stable aqueous emulsion was obtained. The emulsion the dispersoid ShOWn in EXamDle 1 and Wlth, aS Companwas solidified by freezing and the thus obtained solid was son, a dispersoid of a triuorochloroethylene resin by Y 7 i spray coating to form lm -of 0.4 mm. in thickness. The coating conditions and the properties of lm were as follows:

, s position of tetnauoroethylene, ethylene and isobutylene by emulsion polymerization in an aqueous medium comprising Ireacting at a pressure of at least 30 atms'. and at (same as in Example 1) Dispersoid Tetrauoroethylene- Trifluoroehloroethylene ethylenefisobutylene resin dispersoid copolymer dispersoid Coating No 2 times application) Film thickness 0.4 mm 0.4 mm. Chemical resistance (im- Slightly swollen Dissolved.

mersed for hrs. in boiling xylene eontg. 5% HC1).

5 times (containing primer The times of coating treatment `were reduced in the case of using the dispersoid of this invention |while the chemical resistance of ythe lm was excellent.

What is claimed is:

1. A resin copolymer dispersoid composition suitable for coating consisting of particles of a three-component copolymer prepared by anemulsion polymerization of tetrauoroethylene, ethylene and isobutylene and having .the composition in the range of -80 mol percent yof tetrauoroethylene, 20-80 mol percent of ethylene, and 1-49% isobutylene and within the shaded area of FIG. 1 dispersed in an aqueous medium.

2. A resin copolymer dispersoid composition las in claim 1 having the composition in the :area A shown in FIG. 1.

3. A -resin copolymer dispersoid composition as in claim 1 having the composition in the area B Ashown in FIG. 1.

4. A resin copolymer dispersoid composition as in claim 1 having the composition in the area C shown in FIG. 1.

5. A process of producing a copolymer dispersoid coma temperature of -75o C. in the presence of water a gaseous mixture of 20-180 mol percent tetrafluoroethylene, 20-80 mol percent ethylene and 1-49 mol percent isobutylene for la period of several hours until the reaction is complete and recovering said copolymer from the reaction vessel.

6. A process as in claim 5, wherein the emulsion polymerization is carried out in an laqueous medium cont-aining a small amount of alcohol.

7. A process as in claim 5, wherein said recovery process is eected by freezing the copolymer, washing it and then drying in vacuum to result in a finely divided solid.

References Cited by the Examiner FOREIGN PATENTS 588,590 5/ 1947 Great Britain. 5 88,697 5/1947 Great Britain. 680,257 10/ 1952 Great Britain.

MURRAY TILLMAN, Primary Examiner. J. L. WHITE, Assistant Examiner. 

5. A PROCESS OF PRODUCING A COPOLYMER DISPERSOID COMPOSITION OF TETRAFLUOROETHYLENE, ETHYLENE AND ISOBUTYLENE BY EMULSION POLYMERIZATION IN AN AQUEOUS MEDIUM COMPRISING REACTING AT A PRESSURE OF AT LEAST 30 ATMS. AND AT A TEMPERATURE OF 70-75%C. IN THE PRESENCE OF WATER A GASEOUS MIXTURE OF 20-80 MOL PERCENT TETRAFLUOROETHYLENE, 20-80 MOL PERCENT ETHYLENE AND 1-49 MOL PERCENT ISOBUTYLENE FOR A PERIOD OF SEVERAL HOURS UNTIL THE REACTION IS COMPLETE AND RECOVERING SAID COPOLYMER FROM THE REACTION VESSEL. 